Valves include devices for both liquids and gases. Valve actuators for valves are known and may be mechanically operated. For example, the valve actuator may be manually driven, operated by fluid pressure in which the shaft is connected directly or indirectly to a fluid operated piston, or be driven by an electro-hydraulic or electro-fluid means. Conventional valve actuators comprise an electrically driven input shaft, which may be rotatable at relatively high speeds with relatively low torque. The input shaft may, through reducing gears such as a worm gear or a helical screw thread and nut, rotate a relatively high torque, low speed output shaft.
Actuators are often sized such that they can provide more torque than necessary to fully seat a given valve. It may be desirable to determine the torque generated by the output shaft or drive sleeve of a valve actuator. For example, when a valve is fully closed and seated, the torque required to open the valve may be considerably higher. Consistently monitoring the torque may indicate if a valve is wearing out or sticking. Trending patterns in the torque measurements may enable predictive maintenance.
Actuators need to control or limit the amount of torque that can be applied to the load in a manner that is appropriate for various operating modes in a given application. Older mechanical technologies typically operate in either of two modes: active or bypassed. If a torque threshold is exceeded, then the mechanical torque sensor switches the actuator into bypass mode. The torque threshold for switching between modes is fixed by the user at startup and remains fixed until physically changed by the user.
Non-mechanical torque sensors may be used with rotary components; however, the torque sensors would need to be placed on a torsion element in the drive train of the valve actuator. The drive train would be spinning during operation. Therefore, retrieval of the torque information from the spinning sensor would be difficult.
It would be advantageous to develop a technique for measuring the torque generated by a valve actuator without the need to contact a rotating member of the valve actuator.